The key factor in both cases is the wake effect – the way that a rotating turbine and its stand will cause air turbulence, reducing wind velocity for the turbines around it. Or as the Wind Energy Update report’s author, Alan Tricklebank, put it: “The prevalence of wake effects defines a shadow area in which the energy capture of a downwind turbine would be reduced and its fatigue loading increased.”

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Still, ensuring each turbine is completely undisturbed by those around it can be financially unwise. Widely dispersed turbines translate to more occupied seabed; the probability of varying water depths; and increased transmission requirements – all factors that could drive up costs. In the end, “the trick is knowing how to strike the right balance,” Wind Energy Update says.

“The full restoration of the wind from these effects may take 20 rotor diameters or so,” Tricklebank says. “Given that there are costs attached to the area occupied and the transmission distances, it is economic to trade off performance losses against savings in other costs arising from the reduction of the spacing from the aerodynamic ideal.”